1. Field of the Invention
The present invention relates to an image forming apparatus including a photoreceptor and a supplying member arranged to supply the photoreceptor with toner.
2. Description of the Related Art
In a conventional image forming apparatus, such as a copier, a facsimile machine, and a printer, for example, an apparatus using an electro photographic system includes a photoconductive drum on which an electrostatic latent image is formed through laser light and a developing unit arranged to supply the photoconductive drum with toner. As a developing method of the developing unit, a one-component developing method using magnetic toner as developer and a two-component developing method using nonmagnetic toner and magnetic particles (carrier) as developer are used.
The developing unit using the two-component developing method includes a cylindrical magnetic roller and a developing sleeve arranged on an outer circumferential surface of the magnetic roller, both of which serve as a supplying unit that supplies the photoconductive drum with toner. The magnetic roller functions as a carrier adsorbing member, and in this case, because toner is adhered to the carrier, the magnetic roller functions as a toner-and-carrier-adsorbing member. The developing sleeve functions as a member that separates the toner from the two-component developer (mixture of toner and carrier) and attracts the toner to the photoconductive drum. By applying a bias voltage to the developing sleeve, a magnetic field is generated between the developing sleeve and the photoconductive drum, and ears composed of developer are formed on a surface of the developing sleeve. The ears composed of the developer connect with one another along magnetic lines of the generated magnetic field as if the ears are rice ears. Since the density of the magnetic lines is increased in the vicinity of the magnetic roller, the ears are formed in a densely raised state. Only the toner of the ears formed on the developing sleeve is supplied to the photoconductive drum.
In the two-component developing method, an image may greatly change depending on how ears composed of the developer contact with the photoconductive drum (i.e., depending on an angle of the ears relative to the photoconductive drum). Therefore, in the conventional image forming apparatus, in order to maintain a constant position (angle) of ears that contact with the photoconductive drum, a positional relationship between the photoconductive drum and the magnetic roller is fixed by integrating a drum unit and a developing unit into one unit.
However, since the drum unit and the developing unit are integrated into one unit in the conventional art, both units cannot be separated. Therefore, it is difficult to replace only the photoconductive drum, and the drum unit and the developing unit have to be replaced together, which thereby increases the cost.
Since the drum unit and the developing unit are integrated into one unit, when supplying the developing unit with the developer or when removing the developer from the developing unit, operating efficiency decreases.